Method of forming paper from synthetic fibers having a skeletal structure



March 1969 R. s. RIEDESEL METHOD OF FORMING PAPER FROM SYNTHETIC FIBEHAVING A SKELETAL STRUCTURE Original Filed Feb. 5, 1964 United StatesPatent 3 Claims ABSTRACT OF THE DISCLOSURE Preparation of vaporpermeable flexible synthetic leather construction by cuttingmonofilaments which contain ultra fine filaments therewithin, forming adispersion of cut fibers into a mat on a paper machine, drying the matand subjecting same to heat to form continuous skeletal structures fromresin present in the monofilament.

This invention relates to new and very useful mat-like structures and tomethods for making the same. This is a division of application Ser. No.341,913 filed Feb. 3, 1964.

More particularly this invention is directed to non- Woven, moisturevapor permeable, flexible, mat-like structures which have bulk densitylens than the absolute density of the component materials and which areuseful for a wide variety of fabric and coating operations and which canhave physical properties closely resembling those traditionallyassociated with leather. The invention also relates to methods formanufacturing such mat-like structures.

The mat-like structures comprise a uniform mixture of at least twodifferent types of man-made organic polymeric materials. One of thesematerials is in the physical form of ultra fine filaments. Each suchdiscrete ultra fine filament has a maximum cross-sectional dimensionsmaller than about 5 microns. At least 50 weight percent of such ultrafine filaments have ross-sectional dimensions not smaller than about 3microns and minimum respective lengths greater than about 600 micronseach. Preferably at least 50 weight percent of such ultra fine filamentshave respective lengths at least 200 times the maximum cross-sectionaldimension of each ultra fine filament.

The second such polymeric material is in the physical form of acontinuous skeletal structure. Preferably this skeletal structure iscomposel of discrete particles which are bonded to one another (i.e.,interbonded) at their respective points of contact with one another.Each such discrete particle has at least two dimensions less than about5 microns and a third dimension greater than about 5 microns (all suchdimensions being taken perpendicularly to one another). These particlesare substantially solid in physical structure and so are not fibrilatedand not dendritic in the sense of fibrid particles. Preferably theskeletal structure in one class of mat-like structures of this inventioncomprises less than 50 weight percent of the total structure and stillmore preferably between 30 and 50 weight percent.

In a given mat-like structure of this invention, the relationshipbetween the quantity of said ultra fine filaments and the quantity ofsaid particles is such that when, within said structure, substantiallyall of said particles are bonded to one another at their respectivepoints of contact, resulting in a substantially continuous skeletalstructure composed of said second material. Also within 3,433,703Patented Mar. 18, 1969 said structure substantially none of said ultrafine filaments are fused to one another.

The invention is better understood by referring to the attached drawingwherein:

FIGURE 1 is an artists diagrammatic drawing of a photomicrograph of avertical-sectional view through a product of this invention;

FIGURE 2 is an artists diagrammatic drawing of a photomicrograph of avertical-sectional view through another product of this invention; and

FIGURE 3 is an artists diagrammatic drawing of a photomicrograph of avertical-sectional view through a sheet of naturally occurringconventionally tanned leather.

To make the mat-like structures of this invention, one begins withmonofilaments composed of at least two different types of man-madeorganic polymeric materials, such as incompatible thermoplastic resins.Such monofilaments can be made by any conventional means, for example,as taught by US. Patent No. 3,099,067.

By the teachings of this patent one can prepare monofilaments composedof at least two incompatible thermoplastic resins. Each suchmonofilament is characterized by having one of said resins presenttherewithin in the form of ultra fine filaments. Each such ultra finefilament has a generally circular cross-section and is positioned withinits associated monofilament so as to extend generally longitudinallytherewithin. One other of such resins is present within suchmonofilament in the form of a continuous matrix about said ultra finefilaments. While the teaching of this patent relates generally to theuse of two incompatible thermoplastic resins, it will be appreciatedthat by the teachings of this invention one can produce monofilamentssuitable :for use in the products of this invention which contain morethan two incompatible thermoplastic resins per monofilament.

In employing such monofilaments to produce the matlike structures ofthis invention, one first cuts such monofilaments into lengths notgreater than about one-half inch. It will be appreciated that lengthsconsiderably shorter than this are fully within the teachings of thisinvention. The exact length being employed in any given emboliment beingdependent upon the particular type of product one desires tomanufacture.

Next one disperses the resulting cut monofilaments in a liquid medium.The composition of this medium is so chosen as to make the medium atleast a partial solvent for one of the resins composing themonofilaments, preferably that resin which comprises the continuousmatrix portion. Owing to ease of manufacturing, one preferred method ofpracticing this invention is to employ monofilaments wherein thecontinuous matrix is so selected as to be separable from the ultra finefilaments by means of Water as the liquid medium.

Next one agitates the resulting dispersion or slurry until there resultsa substantial separation of each resin from the others comprising themonofilaments being used. By the term substantially separation referenceis had to the fact that the continuous matrix portion of themonofilament tends to separate from the ultra fine filaments to such anextent that usually at least about 50% of the original cut monofilamentsare broken into ultra fine filaments and particles derived from thecontinuous matrix. Preferably separation is substantially complete. Itwill be appreciated that as a result of the separation there is producedat least two classes of materials, depending upon the nature of thecomposition of the starting monofilaments. One class of materialsconsists of the ultra fine filaments which were originally within themonofilaments. Another class of materials consists of discrete particlesderived from the former continuous matrix which was about the ultra finefilaments. If more than two incompatible components are present in thestarting monofilaments there may be more than one class of either ultrafine filaments or discrete particles present in a given dispersion.Also, if one of the components of the starting monofilament is solublein the liquid medium, the product sheet may contain minor, residualamounts of soluble component.

Next the resulting dispersion is formed into a mat by conventionalpaper-making techniques well known to those of ordinary skill in theart. Thus one can deposit the resulting dispersion upon a paper-makingscreen so as to produce a mat. Preferably this mat has a thickness notless than about inch (weight basis). Then the mat can be couched toremove excess liquid. Lastly, the resulting mat can be dried to removeresidual liquid.

Now the resulting mat-like structure is processed so as to interbond atleast one class of the discrete particles present to one another and,possibly, also to other classes of discrete particles which may bepresent, so as to produce a continuous skeletal structure composed ofinterbonded discrete particles.

The bonding of the particles to one another, or the interbonding, can beaccomplished by heat fusion, partial solvation, or any similar techniquewhich fuses at least to an extent sufficient to effect bonding theparticles to one another at their respective points of contact with oneanother. For example, because of ease in processing, one preferredmethod of accomplishing bonding is to use monofilaments wherein thecontinuous matrix can be heat softened and possibly even melted at atemperature sufficiently below the equivalent point for the ultra finefilaments that particles of the continuous matrix material are bondableto one another in a zone of heat which is insufficient to appreciablyalter the physical characteristics of the ultra fine filaments. Thus, itis preferred to use such a combination of incompatible thermoplasticmaterials in the monofilament that the mat-like non-woven structureproduced by paper-making techniques can be subjected to a zone of heatsufficient to bond together one type of resinous particles to otherparticles of the same type so as to produce the desired continuousskeletal structure composed of such particles, the zone of heat usedbeing insufiicient to appreciably alter the physical characteristics ofthe resin composing the ultra fine filaments. The ultra fine filamentsin structures of this invention should be substantially not fused one toanother.

By the term non-Woven as used herein reference is had to the fact thatmat-like structures of this invention consists mainly of materials whichare non-Woven and not made such as by knitting, weaving or the like. Itwill be appreciated, however, that it may be desirable and indeedpreferred for certain applications of the mat-like structure of thisinvention to employ within the mat-like structures of this invention,woven or knit structures which serve to reinforce or otherwise improveproperties desired in final products. However, when such woven materialsare used in making mat-like structures of this invention they generallywill comprise not more than about 20 weight percent of the totalmat-like structure, and indeed, in most cases they will comprise notmore than about 5 weight percent of a total mat-like structure.

One especially useful type of monofilament for purposes of making themat-like structures of this invention comprises a three componentcombination of incompatible thermoplastic resins, to wit, a polyamide,such as Nylon-6, ethylene-vinyl acetate copolymer (such as Elvax 250, aproduct of the Du Pont Corporation) and a non-volatile high molecularweight water soluble polyethylene glycol (such as Carbowax M-20, aproduct of Union Carbide). In monofilaments made from this combinationof incompatible resins, the polyamide becomes the ultra fine fiberswhile the ethylene-vinyl acetate copolymer and the polyethylene glycolpolymer become the continuous matrix. Usually in such a monofilament thepolyamide comprises from about 40-60 weight percent, the ethylene-vinylacetate copolymer from about 20-40 percent and the balance up to in anygiven composition being the polyethylene glycol polymer. Preferably sucha three component monofilament should contain not less than about 5weight percent of the ethylene glycol polymer within the limits abovedescribed. It is a peculiar feature of such a monofilament structurethat when cut up as indicated above in making the mat-like structures ofthis invention that it relatively quickly breaks apart into therespective insoluble resinous components, to Wit, the polyamide and theethylene vinyl acetate copolymer in an aqueous media. Presumably theethylene glycol polymer goes into solution in such media. Thus, it isrelatively easy to make slurries useful for manufacturing the mat-likestructures of this invention by papermaking techniques without the useof costly organic liquids and the problems associated therewith.

Referring to the drawings it will be appreciated that in FIGURES 1 and 2are shown two respective samples of mat-like structures produced inaccordance with the methods taught herein. It is seen that thesestructures are remarkably similar to a similarly sized and magnifiedpiece of natural leather. It Will be appreciated that in these FIGURES 2and 3, numerals With prime marks added thereto refer to similar partsand portions bearing the corresponding numbers in FIGURE 1.

Referring to FIGURE 1 it is seen that the mat-like structure there shownhas a closely packed, relatively smooth face 12, and a rather looselypacked rough back face 14. Within the interior are pores 11 which appearduring the manufacturing process. The embodiment shown in FIGURE 1 hasembedded within it a netted reinforcing web, portions 10 of which can beseen in FIG- URE 1.

In FIGURES 1, 2 and 3 it is seen that the structures are essentiallycomposed of short fibers, the dimensions of the fibers in each casebeing very small.

The invention is further illustrated by reference to the followingexamples:

In these examples the equipment for making the monofilaments employs aA, 16 to 1 length to diameter ratio barrel and screw extruder havingattached to the barrel end thereof an adapter and gear pump followed bya spin pack and spinneret. The spinneret used has 37 holes, each holehaving a diameter of 0.018. The rate of extrusion is about 20 grams perminute. The takeup roll is run at 250 ft./min., and the draw rolls at400 ft./min. The monofilaments produced are wound up on a core using aLeesona winder. A number of these cores of monofilament yarns aremounted on a creel and the individual yarns are gathered into a towwhich is then cut into A" lengths using a conventional cutter.

In each of the succeeding examples the following furnish is used: Theblend of polymers used comprises 50% by weight of a polycaprolactam(e.g. Plaskon 8201, a product of Allied Chemical and Dye Corp., or themedium viscosity polycaprolactam obtainable from American Enka Corp),40% by weight of a copolymer of ethylene and vinyl acetate (e.g. Elvax250, a product of Union Carbide), and 10% by weight of a high molecularweight polyethylene glycol polymer (e.g. Carbowax M-20, a product ofUnion Carbide). Initially the three materials are dry blended bytumbling prior to being fed into the extruder hopper. The temperaturesused in the extruder and spinning assembly are controlled to provide aspinnable extrudate. There is approximately a 10 ft. drop from thespinneret to the takeup Godet and an air quench is used below thespinneret. The yarn obtained is approximately 1470 total deniercontaining 37 filaments with a denier per filament of about 40. A onepound Valley paper beating machine is charged with 400 grams of thisfiber which have been previously cut into lengths, plus approximately 5gallons of water. The fiber is circulated through the machine to wet itout without the use of a bed knife. After 100 minutes the bed knife isapplied and the beater is run for another minutes. The followingexamples are made using this furnish.

Two hand sheets (7" x 7") each weighing 12 grams are prepared by placing1000 cc. of furnish containing 1.2% w. resin solids into a Williams handsheet mold which contains approximately 3500 cc. of water. The drain onthe mold is then opened and the solid materials deposited on a 120-meshscreen. The sheet is removed and dried in a Williams hand sheet drieroperating at about 212. F. Two sheets are each dip-saturated with apolyurethane latex emulsion (e.g. Wyandotte latex E-207), 80 parts ofwhich are diluted with 300* parts of water. Approximately 0.7 gram (dryweight basis) of polyurethane latex solids are retained in each sheet.

The saturated sheets are first blotted dry and then are further dried inan air-circulating oven at a temperature of about approximately 212 F.After drying, the sheets are placed together with one of the screensides contacting the non-screen side of the other sheet. Asmooth-surfaced silicone-coated paper is applied to the exposed screenside face (hereinafter called the face side) of this composite, and a#50 grit Garnet paper is applied to the other face (hereinafter calledthe back side). The composite is then placed in a heated platen press(about 350 F.) for about 30 seconds under a pressure of about p.s.i. Theresulting composite is then withdrawn from the press, cooled, and thesilicone-coated paper and the #50 grit Garnet paper removed. Finally,the resulting laminate is subjected to hand flexing. The back side islightly scuffed with #50 grit Garnet paper.

EXAMPLE 2 This example is prepared in the same manner as Example 1, withthe exception that a urethane-saturated knit fabric is interposedbetween the two laminae. The fabric is knit using a monofilamentextruded in air from a sing e hole spinneret having an opening diameterof about 0.060. The composition of the polymers used is the same,

substantially, as that used in making the monofilaments employed inExample 1.

The monofilament, after coming out of the spinneret, is cooled bypassing through a cold water bath. The residence time in the bath issubstantially less than one-half second. It then passes over a firstGodet roll, then to a second Godet or draw roll driven at a speedapproximately three times faster than the first Godet roll. Themonofilament resulting from the operation is thereby oriented and has afinal diameter of approximately 0.0007.

The knit fabric is then washed with hot water for several minutes afterwhich it is dried on a tentering frame. The fabric is then dip-saturatedwith the polyurethane latex emulsion used in Example 1, after which itis blotted dry and then further dried in an air-circulating oven at 212F. The fabric thus produced has a mesh or loop size of approximatelyEXAMPLE 3 This example is similar to Example 2, however, the hand sheetsare saturated with the polyurethane latex emulsion used in Example 1,however, which is first diluted at a ratio of 80 parts emulsion and 600*parts of water. One of the hand sheets and the knit fabric prepared asin Example 2, are saturated with the polyurethane saturant after whichthey are separately dried as in Example 1. A laminate comprising thesaturated hand sheet, the saturated knit fabric, and an untreated handsheet are placed in a heated platen press (about 350 F.) for about 30seconds, and under a pressure of about 5 p.s.i. The face and back sidesare provided with contacting sheets as in Example 1. The laminate isremoved from the press, cooled, hand flexed and scuffed lightly on theback side.

EXAMPLE 4 This example is made exactly as Example 3, but the saturatingsolution is made using a mixture of 80 parts of the polyurethane latexemulsion of Example 1 and 1200 parts of water.

EXAMPLE 5 The monofilaments used in this example are prepared, as forExample 1, from a dry blend of 50 parts of polyamide polymer (Nylon-6 assold by Spencer Chemical Company), 30 parts of ethylene-vinyl acetatecopolymer (Elvax-250 as sold by the Du Pont Corporation), and 20 partsof high molecular weight polyethylene glycol (Carbowax M-20). Themonofilaments are cut into lengths of and 10 grams thereof, togetherwith 500 grams of water, are beaten in a Waring Blendor for two minutes.Water and excess wax solution are removed by squeezing in a cheeseclothbag after which the dispersed material is beaten together for anothertwo minutes with an additional 500 grams of water. A sheet is formedfrom this furnish by deposition on a 40-mesh screen and roll squeezingout the surplus water. A cheesecloth cover is used during rolling. Thesheet is further dried for one-half hour in an air-circulating ovenmaintained at 150 F. After drying, the sheet is heat-bonded in a platenpress (about 320 F.) for about 30 seconds at about 5 p.s.i. The finishedsheet weighs about approximately 0.3 gram per square inch and has amoisture vapor transmission rate of 1100 grams per square meter per 24hours (using relative humidity on one face and 50% relative humidity onthe other face).

EXAMPLE 6 A non-woven mat-like structure is made using two differenttypes of monofilaments. One monofilament designated (a) comprises apolyamide polymer, an ethylenevinyl acetate copolymer, and a highmolecular weight polyethylene glycol (all polymers as in Example 1). Theother monofilament designated (b) comprises a polyurethane polymer (e.g.Texin-192, a product of Mobay Chemical 00.), an ethylene-vinyl acetatecopolymer, and a high molecular weight polyethylene glycol, the lattertwo polymers being the same as used in Example 1. The first monofilamenthas a dry blend ratio of polymers of 5514015, the second, a ratio of4025525. The monofilaments are made using substantially the same processas is used to prepare the monofilaments for the knit fabric of Example2. Both types of monofilaments are cut into 4; lengths. 18 grams ofmonofilament (a) and 15 grams of monofilament (b), together with 170milliliters of water, are beaten for two minutes in a Waring Blendor.Then, 170 grams of toluene are added and beating is continued foranother three minutes. Approximately grams of liquid is removed from theslurry by hand squeezing in a cheesecloth bag, after which the partiallydried solid ingredients are reintroduced with 600 grams of water intothe blendor and beaten for an additional three minutes. The slurry isthen removed from the blendor and cast onto a 40-mesh stainless steelscreen. After the surplus liquid is roll-pressed out, the sheet is driedfor about one-half hour in an air-circulating oven operating at F. Thesheet is then placed in a heated platen press (about 375 F.), held forabout 30 seconds under about 5 p.s.i. As in Example 1, the face side ofthe sheet is provided with a silicone-coated paper and the back sidewith a #50 grit Garnet paper. After removing the sheet from the press itis cooled and the back side roughened slightly by sanding.

EXAMPLE 7 This structure is made using the same fibers as in Example 6.A 50:50 mixture is prepared of monofilaments which have been cut intoabout /s" lengths. These monofilaments are then dissolved in suflicienttoluene to provide a solution containing 10% solids, based on the totalamount of ethylene-vinyl acetate copolymer present. Dissolving anddispersing of the monofilament solvent blend is aided by shaking for 15minutes on a paint shaker. The slurry thus obtained is then coated ontoa silicone-coated paper and levelling out of the coating is aided by avibrating spreader bar. The coated sheet is then dried in anair-circulating oven operating at 150 F. After drying, the dried sheetis placed in a heated platen press (about 310 F.) for about 45 secondsat about p.s.i. As in Example 1, the face side of the sheet is providedwith a silicone-coated paper and the back side with a #50 grit Garnetpaper. After removing the sheet from the press it is cooled and thenroughened slightly on the back side by sanding. The sample is firstsoaked and then handworked and washed in hot water to remove most of thehigh molecular weight polyethylene glycol material.

What is claimed is as follows:

1. In a process for making a non-woven, moisture vapor permeable,flexible, mat-like structure from monofilaments composed of at least twoincompatible thermoplastic resins, each such monofilament beingcharacterized by having one of said resins present therewithin in theform of ultra fine filaments, each such ultra fine filament having agenerally circular cross-section and being positioned within itsassociated monofilament so as to longitudinally extend therewithin, oneother of such resins being present within such monofilament in the formof a continuous matrix about said ultra fine filaments, the improvementwhich comprises the steps of:

(a) cutting such monofilaments into lengths generally not greater thanabout one-half inch,

(b) effecting substantial separation of each resin from the others in afluid medium, said fluid medium being so chosen as to be at least apartial solvent for one of said resins,

(c) forming a mat from the resulting separated resinous materials bypaper-making techniques,

(d) subjecting the resulting structure to a zone of heat suflicient tobond one type of resinous particles to other particles of the same typeso as to produce a continuous skeletal structure composed of that typeof resinous material, said zone of heat being insufficient toappreciably alter the physical characteristics of other types of resinpresent.

2. In a process for making a non-woven, moisture vapor permeable,flexible, mat-like structure from monofilaments composed of at least twoincompatible thermoplastic resins, each such monofilament beingcharacterized by having one of said resins present therewithin in theform of ultra fine filaments, each such ultra fine filament having agenerally circular cross-section and being positioned within itsassociated monofilament so as to longitudinally extend therewithin, oneother of such resins being present within such monofilament in the formof a continuous matrix about said ultra fine filaments, the improvementwhich comprises the steps of:

(a) cutting such monofilaments into lengths generally not greater thanabout one-half inch,

(b) dispersing the resulting cut monofilaments in a liquid medium, saidliquid medium being so chosen as to be at least a partial solvent forone of said resins,

(c) agitating the resulting dispersion until there results a substantialseparation of each resin from the others,

((1) forming a mat by paper-making techniques, and

(e) subjecting the resulting structure to a zone of heat suflicient tobond one type of resinous particles to other particles of the same typeso as to produce a continuous skeletal structure composed of that typeof resinous material, said zone of heat being insuflicient toappreciably alter the physical characteristics of other types of resinpresent.

3. In a process for making a non-woven, moisture vapor permeable,flexible, mat-like structure from monofilaments composed of at least twoincompatible thermoplastic resins, each such monofilament beingcharacterized by having one of said resins present therewithin in theform of ultra fine filaments, each such ultra fine filament having agenerally circular cross-section and being positioned within itsassociated monofilament so as to longitudinally extend therewithin, oneother of such resins being present within such monofilament in the formof a continuous matrix about said ultra fine filaments, the improvementwhich comprises the steps of:

(a) cutting such monofilaments into lengths generally not greater thanabout one-half inch,

(b) dispersing the resulting cut monofilaments in a liquid medium, saidliquid medium being so chosen as to be at least a partial solvent forone of said resins,

(c) agitating the resulting dispersion until there results a substantialseparation of each resin from the others,

((1) depositing the resulting dispersion upon a papermaking screen so asto produce a mat,

(e) couching such mat to remove excess liquid,

(f) drying such mat to remove residual liquid,

(g) subjecting the resulting structure to a zone of heat suflicient tobond one type of resinous particles to other particles of the same typeso as to produce a continuous skeletal structure composed of that typeof resinous material, said zone of heat being insuflicient toappreciably alter the physical characteristics of other types of resinpresent.

References Cited UNITED STATES PATENTS HOWARD R. CAINE, PrimaryExaminer.

US. Cl. X.R. 162146; 161-172

